Cellerant Therapeutics'goal is to develop a universal off-the-shelf cellular therapeutic of megakaryocyte progenitors (MKP) for the mitigation of irradiation-induced thrombocytopenia. These progenitors will be derived and expanded ex vivo from hematopoietic stem cells (HSC) (CD34+ cells) in serum and animal product free medium. Within the scope of this grant we are planning to define culture conditions and a production process for the mass manufacturing of MKP cells. Megakaryocyte progenitor populations have been described both in mouse and men. Of particular interest are mouse studies demonstrating that relatively few isolated MKP alone can significantly raise blood platelet counts and contribute to platelets in circulation for almost 4 weeks. In human autologous peripheral blood stem cell transplants it has been noted that platelet recovery correlates with the number of CD34+CD41+ MKP. We propose to produce these cells ex vivo using either umbilical cord blood or G-CSF mobilized peripheral blood stem cells as the starting population. MKP cells will be derived from multiple donors, pooled and cryopreserved. Therefore large doses can be stockpiled and will readily be available in case of accidental or warfare related exposure to radiations. We believe that megakaryocyte progenitors can be used without any HLA-matching by simple infusion to a victim of irradiation and that a single dose will be sufficient to provide rapid and over 3-4 weeks sustained platelet recovery without causing long term engraftment. As indicated by our animal radioprotection experiments one of the major advantages of this approach will be that this therapeutic remains effective even when applied up to 4 days post the irradiation event. Furthermore, this therapy can be combined with current standards of care for irradiation victims and will likely act synergistically with approaches using growth factors for the stimulation of platelet production since it provides additional uninjured progenitors to the victim's hematopoietic system. Therefore, this cellular therapeutic has the potential to dramatically increase the survival and reduce the medical care for victims who have been exposed to doses of 2-6 Gy of radiation. Within the scope of this proposal, Cellerant plans to develop culture conditions for the optimal expansion of MKP ex vivo using serum-free and chemically defined products. We will also evaluate different sources for CD34+ hematopoietic stem cells as the starting material for MKP expansion cultures. Once culture conditions are established we will define a manufacturing process for the large scale production of cryopreserved MKP. This will include development of cryopreservation/thawing procedures for the long-term storage of MKP cells. We will also establish and qualify in vitro and in vivo assays to analyze the cell product for platelet potential and production of functional mature platelets. These assays might later on be used as product release and potency assays for subsequent phases of clinical studies. Lastly, we will initiate in vivo safety studies to test the MKP cellular therapeutic for developmental potential, infusion related toxicity, persistence, and tumorigenicity. Upon completion of these objectives Cellerant is planning to execute pre-clinical toxicology studies and initiate clinical trials. Any exposure to irradiation >1 Gy will lead to temporary damage of the hematopoietic system including the depletion of platelets in blood circulation. This situation of thrombocytopenia is putting victims of accidental or warfare related irradiation at risk of uncontrolled bleeding. Cellerant Therapeutics Inc. is proposing to develop a cellular product consisting of megakaryocyte progenitors MKP that can be administered several days post exposure to radiation to provide platelet support. To achieve this goal we are proposing to accomplish the following objectives: Aim 1. Establish ex vivo culture conditions for the expansion of MKP. Under this aim we will first establish optimal culture conditions for the expansion of MKP, identify the best cellular source for the CD34+ starting material, and develop processes for the large-scale production and cryopreservation of MKP. This work is expected to take 12 months. Aim 2: Demonstrate functional production of platelets from MKP. The objective of this aim will be to perform in vitro and in vivo functional assays to evaluate the MKP cell product developed under Aim1 for platelet potential and show that functional platelets can be derived in relevant numbers from cryopreserved MKP product. The expected time line to achieve this goal is 6 months. Aim 3: Demonstrate Safety and determine immunogenicity of human MKP. In parallel with Aim 2 we will initiate in vivo safety studies using the NOD/scid and nude xenograft mouse models to test pooled allogeneic and cryopreserved MKP cells for toxicity, long-term persistence, and tumorigenicity. These studies might extend beyond the funding period depending on the observed persistence but it is expected to collect at least 3 months data within the funding period. In addition we will analyze the immunogenicity of MKP cells using in vitro assays. We believe it is feasible to develop a commercially viable, storable and universal cell product that will provide physiological relevant numbers of platelets upon transfusion into thrombocytopenic patients. Completion of these proposed goals should enable Cellerant to move this potential product close to initiate IND enabling pre-clinical toxicology studies and subsequently Phase I clinical trials.